1. Field of the Invention
This invention relates to an improved process for the preparation of butynediol by the reaction of acetylene and formaldehyde. More specifically, this invention relates to an improved process for the preparation of butynediol by the reaction of acetylene and formaldehyde in the liquid phase in the presence of an insoluble particular copper complex catalyst and a sodium carbonate-sodium bicarbonate buffer.
2. Description of the Prior Art
The preparation of butynediol by the reaction of formaldehyde and acetylene in the presence of a slurry of copper acetylide catalyst is described in British Pat. No. 698,019 and U.S. Pat. Nos. 2,939,844 and 3,154,589. An improved catalyst and process for the production of butynediol is described by Kirchner is U.S. Pat. Nos. 3,650,985 and 3,560,576. In the Kirchner patents it is disclosed that the pH of the reaction mixture during the ethynylation reaction may be maintained by ion exchange or acid acceptor treatment of the feed. Calcium carbonate is disclosed as an acid acceptor. Sodium carbonate and sodium bicarbonate have also been used for controlling pH during the ethynylation reaction.
At 90.degree. to 100.degree. C formaldehyde tends to disproportionate to methanol and formic acid. The presence of calcium results in the formation of calcium formate. Calcium formate, in the subsequent processing of crude filtrate from the butynediol reactor involving the stripping of formaldehyde and the hydrogenation of the residue directly over an activated nickel aluminum alloy catalyst to form an aqueous solution of butanediol, decomposes to insoluble calcium salts which foul heat exchanger surfaces and produces deposits on the hydrogenation catalyst causing a loss in activity.
Because of the above problem it has been customary to employ sodium bicarbonate to control the pH in such reactions. A major disadvantage of the bicarbonate salt is the generation of carbon dioxide which dilutes the recycle acetylene. A substantial purge of the recycle gas is required to maintain acetylene concentration, which results in substantial acetylene losses.